JPH0429766B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is a method for producing precursor fibers for producing carbon fibers, and is particularly suitable for producing carbon fibers with excellent quality and physical properties, as well as markedly improving process passability during the production of carbon fibers. The present invention relates to a method for producing a precursor fiber for carbon fiber production (hereinafter referred to as a precursor). (Prior art) Carbon fiber is made of acrylic precursor,
Rayon-based, pitch-based, or polyvinyl alcohol-based fibers are converted into oxidized fibers by heating and baking in air at 200 to 400°C or in an oxidizing atmosphere such as nitrogen oxide (flame-retardant process), and then treated with nitrogen, argon, helium, etc. It is obtained through a method of carbonization by further heating at a high temperature of 300 to 2000℃ in an inert atmosphere (carbonization process), and due to its excellent physical properties, it is widely used in many applications, especially as a reinforcing fiber suitable for composite materials. has been done. However, in the above-mentioned industrial manufacturing method of carbon fibers, there is a problem that fusion occurs between single fibers in the flameproofing step of converting the precursor into oxidized fibers and the subsequent carbonization step. If this fusion of single fibers occurs, it will not be possible to fire the fibers uniformly, causing fuzz and thread breakage, which will not only be a major cause of hindering process passability, but also carbon fibers with excellent quality and physical properties. It becomes impossible to manufacture. Therefore, in order to prevent such fusion between single fibers, many methods of improving the oil agent to be applied have been disclosed. For example, a method of applying a specific oil, especially a silicone oil
No. 52-24136, Special Publication No. 51-12739, Japanese Patent Publication No. 1983-
No. 99011, JP-A-58-214517, JP-A-52-
148227 publications), further improved heat resistance,
Alternatively, a method of applying an oil with specified heat resistance (for example, Japanese Patent Publication No. 58-5287, Japanese Patent Application Laid-open No. 60-146076,
JP-A-59-66518, JP-A-58-120819, JP-A-55-103313), and so on. However, with the above method, these can be done independently,
Alternatively, even if various combinations were used, fusion between single fibers could not be sufficiently prevented, and these were insufficient as means for preventing fusion. On the other hand, it is possible to prevent fusion by lowering the temperature of the atmosphere during the firing process, but in this case, it is also necessary to slow down the processing speed, resulting in a decrease in production efficiency. Therefore, it cannot be used as an industrial means of production. (Problems to be Solved by the Invention) The purpose of the present invention is to prevent the fusion of single fibers that occurs during the firing process, and to produce carbon fibers that are of high quality and have excellent physical properties. An object of the present invention is to provide a method for producing precursor fibers for use in industrial applications. (Means for Solving the Problems) The above object of the present invention is that the alicyclic epoxy group is 0.05
-10% by weight of a silicone-based oil having a viscosity of 1,000-15,000 centistokes at 25°C, which is applied in an amount of 0.01-5% by weight based on the weight of the fiber, for manufacturing carbon fibers. This can be achieved by a method for producing precursor fibers. The silicone oil used in the present invention is characterized by the addition of an alicyclic epoxy group, and the alicyclic epoxy group includes a 1,2-epoxy-cyclohexyl group (the following structural formula), A typical example is a 1,2-epoxy-cyclobentyl group (the following structural formula). Examples of the silicone oil agent to which the alicyclic epoxy group of the above structural formula () is added include those having the following structural units. (Here, n ₁ is a positive integer of 1 to 5, and n ₂ is 0 or 1. R ₁ to _{R 9} are hydrogen atoms and/or alkyl groups.) Here, the silicone oil agent of the present invention The basic skeleton of
It has a siloxane bond, -Sio-, and the silicon atom, the group bonded to Si (for example, R in the above structural formula) is a hydrogen atom or/and an alkyl group having 1 to 3 carbon atoms, a phenyl group, or an alkoxy group thereof. Examples include basics. Among these, dimethylsiloxane is particularly preferred as the basic skeleton. Several proposals have already been made regarding silicone oil agents to which epoxy groups have been added in order to prevent fusion between single filaments during the carbon fiber firing process. For example, in Japanese Patent Publications No. 18334/1983, No. 181322/1982, and No. 181323/1989, a glycidyl type epoxy group (not an alicyclic epoxy group) is added alone. Also disclosed is a method of applying it by mixing it with other modified silicone oils. However, although these methods have the effect of preventing fusion between single filaments during the firing process, the effect is not sufficient;
This was insufficient to prevent fusion between single yarns and to produce carbon fibers of excellent quality, which is the objective of the present invention. When the dimethylsiloxane-based oil of the present invention having the above-mentioned structural characteristics is applied, the fusion between single fibers is stronger than that of the previously disclosed glycidyl-type epoxy group-added oil. The present inventors have discovered that the effect of preventing this is greater, leading to the present invention.The reason for this is that the presence of an alicyclic group increases the affinity of the oil component for the fiber matrix. This is thought to be because the film is formed uniformly and firmly. The amount of alicyclic epoxy group added is epoxy group
The amount is 0.05 to 10% by weight, preferably 0.1 to 5% by weight, calculated as CH ₂ CH ₂ O. If the amount is less than 0.05% by weight, the effect of the alicyclic epoxy group will not be exhibited, and fusion between single fibers cannot be effectively prevented. On the other hand, if the amount added exceeds 10% by weight, the heat resistance of the oil component itself decreases, and fusion between single fibers cannot be effectively prevented. The siloxane skeleton of the alicyclic epoxy group of the present invention,
That is, the bonding mode for -SiO- may be such that it is continuously bonded to adjacent Si parts in a block shape (for example, the bonding state shown in A below), or it is not bonded to adjacent Si parts. They may be in a state where they are not bonded (for example, a bonded state as shown in B below), or a combination of these bonded states. In short, it is sufficient that the above-mentioned addition amount of alicyclic epoxy group is 0.05 to 10% by weight. (E represents a modifying group containing an alicyclic epoxy group.) A substituent bonded to the ring group of the alicyclic epoxy group added to the silicone oil agent of the present invention (for example, R ₁ to R in the above structural unit) R ₉ ) is a hydrogen atom and/or an alkyl group. Examples of the alkyl group as a substituent include an alkyl group having 1 to 3 carbon atoms, and all of these substituents may be the same or different from each other, but there are no particular limitations. It is not something that will be done. The viscosity of the dimethylsiloxane oil agent to which the alicyclic epoxy group of the present invention is added is measured at 25°C.
1000 to 15000 centistokes (abbreviated as cs), preferably 2000 to 12000 cs. If it is less than 1000 cs, the heat resistance will be low and it will not be possible to prevent fusion between single yarns. If it exceeds 15,000 cs, it becomes difficult to disperse it in water or find a solvent with excellent solubility, making it impossible to apply it uniformly to the surface of the yarn. In the oil agent of the present invention, heat resistance is an important property, and it is preferable to use an oil agent that has a viscosity in the above range and structural characteristics, and has a heat resistance residual rate (r) of 20% or more. It is more preferable to use one with a content of 30% or more. Here, the heat resistance residual rate r shall be defined below.
In other words, the residual rate when heat treated in air at 240°C for 60 minutes is r ₁ (%), and the residual rate when subsequently heat treated in nitrogen at 450°C for 30 seconds is r ₂ (%).
Then, r=r ₁ ×r ₂ /100 (%). (Measurement method will be described later) The flame-retardant process of converting the precursor into oxidized fiber in the firing process is an oxidation treatment process of the yarn at a high temperature of 200 to 400℃, and the heat resistance of the oil agent present on the surface of the yarn is If it is bad, the oil component applied to the surface of the yarn will decompose and volatilize during this step, making it impossible to prevent the yarn from fusing. In the carbonization step under an inert atmosphere that follows the flameproofing step, for example, when acrylic fibers are fired, in the first half of the carbonization step, a network structure of naphthyridine rings formed in the flameproofing step is formed, and the carbonization It is said that in the latter half of the process, a higher-order structure of this network structure is formed and grows. The first half of this carbonization process, i.e. 400-500
The present inventors have found that during the process of increasing the temperature to .degree. C., the single fibers still tend to fuse together, and the fusion does not occur until the latter half of the process. As described above, the ability of the oil component to prevent the single fibers from adhering is an essential property not only in the flameproofing process but also in the first half of the carbonization process. In order to increase the affinity of Bricasa for the substrate, it is a feature of the present invention that it has an alicyclic epoxy group. It is preferable to have the following. These oil components can be used by being emulsified and dispersed in water by using a suitable emulsifier, or can be applied as a solution dissolved in a suitable solvent such as water or an organic solvent. The amount of these oil components applied to the yarn is based on the weight of the yarn,
It is preferable to add 0.01 to 5% by weight, preferably 0.1 to 3% by weight. If the amount applied is less than 0.01% by weight, the object of the present invention cannot be achieved, while if it exceeds 5% by weight, the stickiness of the oil component will increase during baking,
It is undesirable that a large amount of thermal decomposition residue of the oil component remains on the surface of the yarn, and that problems such as volatile matter depositing during the process occur, deteriorating the physical properties and productivity of the carbonized yarn. Precursors to which the oil component of the present invention can be applied are not particularly limited, such as acrylic, rayon, pitch, and polyvinyl alcohol precursors. It is possible to prevent the fusion of single fibers that occurs at the same time, and it is particularly effective when applied to acrylic fibers. An example of application to acrylic fibers will be described below. The acrylic fiber that can be preferably used in the present invention is acrylonitrile (hereinafter referred to as AN).
containing AN as a main component, preferably 94% by weight or more, particularly preferably 97% by weight or more,
A copolymer of AN and a vinyl group-containing compound (hereinafter referred to as vinyl monomer) that is copolymerizable with AN and promotes a flame-retardant reaction, preferably at most 6% by weight, particularly preferably at most 3% by weight. is used. Examples of vinyl monomers that promote flame resistance include acrylic acid, methacrylic acid,
Examples include itaconic acid, alkali metal salts and ammonium salts thereof, α(1-hydroxyethyl)acrylonitrile, and acrylic acid hydroxyester. In addition to these vinyl monomers that have the ability to promote flame resistance, lower alkyl esters of acrylic acid and methacrylic acid, allyl sulfonic acid, methallyl The total amount of copolymerized components of sulfonic acid, styrene sulfonic acid and their alkali metal salts, vinyl acetate, vinyl chloride, etc. is 6% by weight or less, preferably 3% by weight.
Copolymerization may be carried out within a range of % by weight or less. AN-based copolymers are polymerized using known emulsion suspension, bulk, and solution polymerization methods, and when producing acrylic fibers from these polymers, dimethylformamide, dimethyl sulfoxide, and nitric acid are used. , a polymer solution such as Rodanzoda aqueous solution is used as a spinning stock solution, and conventional wet spinning method, dry spinning method, etc.
It can be spun into fibers by wet spinning or dry spinning. In particular, when a dry-wet spinning method is used, fusion between single fibers is more likely to occur, so the effects of the present invention are more pronounced. The oil agent of the present invention may be applied during the yarn spinning process, or after yarn spinning, during the firing process, but
In order to uniformly apply the precursor to the precursor, it is preferable to apply it during the spinning process. Particularly in the case of acrylic fibers, it is preferable to apply it to yarns in a water-swollen state before drying and densification. Application methods include immersing the yarn in a dispersion or solution of the oil agent and then adjusting the amount of adhesion to a predetermined level by spraying with a nip roller or compressed air, or bringing it into contact with a roller moistened with the oil agent. Alternatively, it can also be applied in the form of a mist using an atmospheric atomization method. In addition, in the present invention, other oil components may be added in addition to the silicone-based oil of the present invention, if necessary, for preventing the generation of static electricity or for other purposes. (Effects of the Invention) The precursor fiber for carbon fiber production obtained by the method of the present invention has the following properties:
Fusing between fibers can be largely avoided, making it possible to produce carbon fibers with excellent process passability, high quality, and high performance. The present invention will be explained in more detail with reference to Examples below. In addition, in the text and examples, the performance (strength, elastic modulus) of carbon fiber is the physical property of a strand impregnated with epoxy resin measured according to JISR-7601, and was determined from the average of n = 10 measurements. It is a value. The amount of the oil component attached was determined by extraction from the fibers after application of the oil agent but before drying and densification. Further, the heat resistance residual rate r based on the above definition was measured by the following procedure. (A) Pretreatment of oil agent Before starting the above heat treatment operation necessary for measuring the heat resistance residual rate, collect 1 g of oil agent into an aluminum container with a diameter of approximately 60 mm and a height of approximately 20 mm, and place it in an oven. Dry at 105℃ for 5 hours. (B) Measurement using a differential thermal analyzer (TGA)
Collect 15 to 20 mg into a cylindrical aluminum container (pan) with a height of 5 mm and determine the heat-resistant residual rate using a differential thermal analyzer (TGA). Measurement conditions, etc. are described below in (C) to (F). (C) Calculate the residual rate from the remaining amount of the oil when the temperature is raised to 240°C under a stream of air under the following heating conditions and further treated at 240°C for 60 minutes. The residual rate at this time is defined as r ₁ (%). Air flow rate: 30l/min Temperature increase rate: 10°C/min (D) After completing the heat treatment at 240°C for 60 minutes in (C), the heating atmosphere was changed from air to nitrogen while maintaining the temperature at 240°C. Hold for 5 minutes. Nitrogen flow rate: 30 l/min (E) Raise the temperature from 240°C to 450°C under the following heating conditions, hold at 450°C for 30 seconds, and determine the residual rate r ₂ (%). Nitrogen flow rate: 30l/min Temperature rising rate: 10℃/min (F) The heating residual rate r ₁ in air and the heating residual rate r in nitrogen determined in (C) and (E) above ₂ , the heat resistance residual rate r of the oil agent is determined from r=r ₁ × r ₂ (%). Example 1 A dimethyl sulfoxide (DMSO) solution of a copolymer of 99.0% AN and 1.0% itaconic acid was used as a spinning dope. The concentration of the copolymer in this stock solution was 20% by weight, and the intrinsic viscosity of the copolymer was 1.80. This spinning dope was once discharged into the air using a nozzle with a diameter of 0.15 mm and 3000 holes, passed through a space of about 3 mm, and then introduced into a 30% DMSO aqueous solution and solidified. This coagulated yarn was desolvated in a water washing tank and then stretched 3.5 times in hot water to obtain water-swollen acrylic fibers (hereinafter referred to as bath-drawn yarn). A dimethylsiloxane-based oil component containing an epoxy group-bonded skeletal unit represented by the following structural formulas (1, the present invention) and (2, not the present invention) is added to the bath-drawn yarn using ethylene oxide of nonylphenol. They were applied individually by dispersing and emulsifying them in water with a nonionic surfactant mainly consisting of adducts. The viscosity of the oil component applied here at 25℃ is
Both were 4500 to 5000 cs, and the amount applied to the fibers was set in the range of 1±0.2% by weight by adjusting the concentration of the oil bath. The yarn obtained in this way after applying the oil agent,
Drying and densification treatment was performed using a heated roller at 130°C. The yarn after drying and densification was further drawn 3 to 4 times in saturated steam at 3 kg/mm ² -G. The precursor fiber thus obtained had a single denier of 0.8 de, total denier of 2400 De, strength of 6.5 to 7.5 g/d, and elongation of 10.5 to 12.0%. This precursor fiber is flame-resistant treated in a flame-proofing furnace with a temperature gradient of 250 to 280°C (processing time = 25 minutes).
Then, it was converted into carbon fiber by firing in a carbonization furnace with a temperature gradient of 300 to 1300°C under a nitrogen atmosphere. The strand strength of the carbon fibers thus obtained is shown in Table 1.

【table】

[Table] Example 2 In the structural formula (1) of Example 1, the viscosity at 25°C is
7000cs, an oil component having an epoxy modification amount of 1.5% by weight with alicyclic epoxy groups was applied. Carbon fibers were obtained in the same manner as in Example 1, except that the amount of oil component applied to the yarn was changed. Table 2 shows the applied amount and the strand strength of the carbon fiber.

[Table] Example 3 In structural formula (1) in Example 1, oil components with different viscosity at 25°C and the amount of addition of epoxy groups were applied. By the same method as in Example 1, the carbon fibers were applied to bath-drawn yarn to obtain carbon fibers. Table 3 shows the viscosity, amount of modification, and heat resistance r, as well as the strand strength of the carbon fibers.

【table】

【table】

Claims (1)

[Claims] 1. A silicone oil containing 0.05 to 10% by weight of alicyclic epoxy groups and a viscosity of 1,000 to 15,000 centistokes at 25°C is attached to the fiber in an amount of 0.01 to 5% by weight based on the weight of the fiber. A method for producing a precursor fiber for carbon fiber production, characterized by: